Polycarbonate resins are used in a wide variety of fields because of their excellent transparency, heat resistance, mechanical properties, dimensional accuracy, etc. For example, molded products are produced by injection molding, extrusion, or the like of polycarbonate resin flakes, and are widely used in optical applications such as optical lenses and films. However, with an increase in size of molded products made of polycarbonate resins (hereinafter, simply referred to also as “molded products”), and an increase of use in applications for allowing light to be incident in parallel to a plane such as light guide plates, higher transparency is being required in molded products. That is, coloration of molded products into yellow (in particular, amber color) has become more noticeable, and use of conventional molded products in applications that require high transparency is becoming difficult.
In order to solve such a problem, Patent Literature 1, for example, proposes a method of performing a pretreatment in the synthesis of a polycarbonate resin. Patent Literatures 2 and 3 disclose techniques for controlling the oxygen concentration in the synthesis. Patent Literature 4 discloses a technique for blending an antioxidant to a polycarbonate copolymer. Patent Literature 5 discloses a polycarbonate resin to which a phosphorus compound having a specific oxidation number is added. Patent Literature 6 discloses a technique for performing deoxygenization on a resin raw material before melt-kneading and/or during melt-kneading in a method for producing processed products of an extruded resin. Patent Literature 7 discloses a technique for feeding an inert gas into a heating cylinder provided in a molding device. However, in the current situation, the aforementioned problem cannot be said to be sufficiently solved only by these methods.
As another technique for enhancing the transparency, Patent Literature 8 discloses that a thermoplastic resin is stored with oxygen being blocked. However, even if blocking oxygen can suppress the coloration of the thermoplastic resin with a lapse of storage time to prevent hue deterioration, the hue is not improved as compared with when the thermoplastic resin is produced. Accordingly, inherent hue improvement of the thermoplastic resin is difficult only by improving the storage condition.
As described above, the problem of transparency due to the coloration of molded products cannot be necessarily solved reliably by conventional methods. Therefore, there has been a demand for providing a polycarbonate resin or a composition thereof that can prevent the coloration more reliably (hereinafter, referred to also as “polycarbonate resin (composition)”), a method for producing a molded product thereof, and a polycarbonate resin (composition) molded product that sufficiently suppresses the coloration and has excellent transparency.
Meanwhile, recent studies in the field of medical care have gradually revealed that light in the ultraviolet region and light in the short wavelength region of visible light have adverse effects on eyes and body. In particular, LED is recently used for illumination and light sources of backlight for liquid crystal displays, and the frequency of exposure to the light in the short wavelength region of visible light has increased. Therefore, eyeglass products having a function of absorbing or reflecting the light in the ultraviolet region and light in the short wavelength region of visible light are put on the market. Further, in order to prevent the light in the ultraviolet region and light in the short wavelength region of visible light out of the rays emitted from liquid crystal displays such as personal computers or televisions from entering eyes, front surface plates for displays that absorb and block the light in such regions have been developed.
Conventionally, in order to block light in the ultraviolet region and light in the short wavelength region of visible light, a resin composition to which a dye that absorbs the light in such regions is added, a molded product on which a film that reflects the light in such regions is laminated or which is coated with a reflective layer, and the like have been developed to be applied to eye glasses and the like (for example, Patent Literatures 9 and 10). However, these methods are costly due to the need for the dye or additional members for reflection. Further, due to the need for a dye mixing step, a reflection film laminating step, and a reflective layer coating step, the production process becomes complicated. In particular, in a method of adding the dye, the dye bleeds out of the resin, which can cause problems such as contaminating the surface of the molded product and reducing the ray blocking performance. Further, some of ultraviolet absorbers are designated as Type I specific chemical substances because of their toxicity, and therefore active use thereof is not desirable. Meanwhile, the methods of laminating a reflection film and coating with a reflective layer can have problems such as delamination, cracking, and uneven coating. Accordingly, a polycarbonate resin (composition) that can solve these problems and can block light in the ultraviolet region and light in the short wavelength region of visible light, and a molded product thereof are desired.